Terrestrial plants don’t like being underwater for long periods of time – as farmers across the UK have found out to their cost in the past few months. But aquatic plants are not designed to “work” out of the water either. Normally, the aquatic environment supports much of the weight of the plant and consequently, aquatic plants don’t devote as much of their resources to the sort of structural tissues required to hold up land plants.
But what about plants from environments where the water level routinely fluctuates? Wetlands are impacted by hydrological regimes that can lead to periods of low water levels. During these periods, aquatic plants experience a drastic change in the mechanical conditions that they encounter, from low gravitational and tensile hydrodynamic forces when exposed to flow under aquatic conditions, to high gravitational and bending forces under terrestrial conditions. The objective of this study was to test the capacity of aquatic plants to produce self-supporting growth forms when growing under aerial conditions by assessing their resistance to terrestrial mechanical conditions and the associated morpho-anatomical changes.
A recent paper in Annals of Botany investigates the capacity of aquatic plants from eight genera to produce self-supportive phenotypes capable of resisting terrestrial mechanical conditions.
They find that six species show higher stiffness in bending, either as the result of an increased allocation to strengthening tissues or by an increase in cross-sectional area in the organs bearing the mechanical forces. These plastic responses may play a key role in the ability of the species to colonize highly fluctuating environments, but reduced capacity for plants to tolerate aquatic mechanical conditions when water level rises again could represent a cost of producing a growth form adapted to aerial conditions.